In image forming apparatuses such as a copying machine, a printer, a facsimile, and the like, various members to be rotated are used for image forming processing. For example, in an image forming portion of an electrophotographic system, a photosensitive drum is placed, and rotation members such as a transfer roller and a cleaning roller are provided in contact with the surface of the photosensitive drum. The photosensitive drum and the members to be rotated are rotatably driven at a predetermined velocity (rpm), and an image is formed through processes such as charging, exposure, toner image formation on the drum surface, transfer of a toner image onto paper, and cleaning of a drum surface.
In order to rotate the above-mentioned members to be rotated at low velocity with a high precision, a rotation drive apparatus having a motor, and a velocity reduction gear for reducing the revolution of the motor, and a velocity detection mechanism for detecting the revolution of the motor is required. As the velocity detection mechanism, a configuration using an encoder and an optical sensor as described in JP 06-327278 A is generally used.
Conventionally, the velocity detection mechanism is attached directly to a drive output shaft and a drive roller outside of a unit without being protected with a housing or the like. Therefore, there is a fear in that foreign matters such as lubricating oil and abrasion powder may adhere to an encoder and a sensor to cause a reading defect of the sensor. Further, the setting space in a direction of the rotation shaft is also required, and hence assembly operability is poor. Further, because the encoder and the sensor are fixed, it is difficult to adjust the gap between the encoder and the sensor. For example, in the case where the members to be rotated are rotated while the encoder and the sensor are in contact with each other, there is a problem in that abrasion of the encoder may occur.
Then, a method of reducing the contamination of the encoder and the sensor, reducing space requirements, and enhancing assembly operability has been proposed, and JP 2003-23755 A discloses a rotation drive apparatus in which a velocity detection mechanism is accommodated in a housing together with a velocity reduction apparatus, and a window portion for adjustment for adjusting the attachment position of a detection unit to the housing is provided.
However, according to the method of JP 2003-23755 A, a housing structure in which a velocity-reducing mechanism is separated from a velocity detection mechanism is used, and support bearings of an output shaft are set on a partition wall surface that separates an outer wall surface of the housing from the inside of the housing. Therefore, the intervals between the support bearings are short, and the tilt of the output shaft may be increased depending on the size error of the support positions of the bearings. Further, the housing is separated into a first member and a second member, and hence it is necessary to enhance a molding precision of the housing as well as an alignment precision, which is inconvenient in terms of production and cost.
Further, in order to prevent contact between the encoder and the sensor, it is necessary to adjust the position of the sensor in the shaft direction. However, the adjustment of the attachment position of the detection unit described in JP 2003-23755 A relates to a position adjustment in the radial direction of the encoder, while a position adjustment in the shaft direction is not described.